The "worth" of the worth four dot test.

Worth's four dot test was first described one hundred years ago. Despite many technological advances in equipment and techniques during the last century, this simple test is still used routinely by many strabismus specialists. It is an invaluable test when used in the evaluation of longstanding and acquired strabismus in adults and in the management of complex diplopia. Techniques using the test include selecting an optimal prism, assessing the effect of a prescribed prism or compensatory head posture on the range of binocular single vision, identifying non-organic responses, diffe1rentiating monocular from binocular diplopia, especially when they co-exist, and blurred from double vision in older patients with divergence paresis. It also can be used with prisms preoperatively to determine the risks of postoperative diplopia and give clues to the presence of torsion or a visual field defect.